Chlorine dioxide is utilized in a variety of processes including a large number of bactericidal applications, especially in the fields of water treatment and odor abatement. Its usage is continuing to grow for many reasons. Due to the unstable nature of gaseous chlorine dioxide when compressed, it is necessary to produce chlorine dioxide on site rather than to produce it at a plant and ship it for usage when needed. A state of the art process involves the production of chlorine dioxide by the reaction of a chlorinated water stream with an alkaline chlorite, followed by the introduction of the generated chlorine dioxide from such reaction into the particular material or system to be treated.
The prior art is filled with disclosure on various types of chlorine dioxide generators, most of which comprise elongated glass or plastic columns of various constructions. Reference is made, for instance, to U.S. Pat. No. 4,013,761, issued to Olin Mathieson.
Another apparatus known to applicant is that of Westerlund as disclosed in U.S. Pat. No. 3,502,443.
Still another chlorine dioxide generating system is disclosed in the Fuller et al. U.S. Pat. No. 3,816,077, which employs sodium chlorate, sodium chloride and acid for the production of chlorine dioxide.
In addition, applicant is aware of the fact that the Wallace and Tiernan Division of Pennwalt Corporation is engaged in the design and manufacture of chlorine dioxide generators.
All of the prior art chlorine dioxide generators which have employed columns, tend to be large and bulky. They require the usage of chemical feed pumps to meter in the raw materials utilized for the process. One of the problems associated with such prior art units is the inadequacy of the mixing to achieve conversion from the raw materials being employed to chlorine dioxide.
Another problem that is encountered when using state of the art generators of the column type, especially when employing low chlorine dioxide feed rates, or when utilizing water that is highly alkaline, and especially when gaseous chlorine is used as one of the reactants, is that the hydrolysis of the chlorine into HOCl become difficult. Furthermore, the generation reaction operates inefficiently when the pH is not in the neighborhood of 3 to 4. Ofttimes excess chlorine and/or a third chemical, such as a mineral acid, must be added to bring the pH into such a range. Obviously, the additional reactant for the pH maintenance introduces more cost to the process. Furthermore, when gaseous chlorine is unavailable and a three chemical system utilizing sodium chlorite, sodium hypochlorite and hydrochloric acid or some other nonoxidizable mineral acid must be used, the present invention can still be employed utilizing less acid than in the prior art systems, thus rendering a three chemical system more cost effective.
It has now been discovered that the problems of the prior art generators can be overcome and that a superior method of generating chlorine dioxide may be achieved by the utilization of the apparatus of the present invention.
It is therefore on object of this invention to prepare chlorine dioxide from a two chemical reaction in the apparatus of this invention.
It is also an object of this invention to prepare chlorine dioxide by a three chemical reaction when gaseous chlorine is unavailable, utilizing the apparatus of this invention.
Another object of the invention is to provide a process for the preparation of chlorine dioxide that is cost effective.
Yet another object is to provides an apparatus for the in situ generation of chlorine dioxide from a concentrated aqueous alkaline chlorite source.
A yet further object is the provision of the apparatus which can be constructed at low price without the necessity of a large column and which takes up minimal space in a treatment plant.
Still another object is to provide a substantially safe chlorine dioxide generation system that avoids large build ups of undiluted ClO.sub.2.
A still further object is to provide a chlorine dioxide generation system of high efficiency under varying water conditions.
Other objects will in part be obvious and will in part appear hereinafter.